Hydroacoustic amplifier



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ITUTE FOR MISSING XR Aug. 19, 1969SUBST R SELSAM ET AL 3,461,910

HYDROACOUSTIC AMPLIFIER Filed June 2. 1966 r INVENTORS ROGER L. SELSAM MAX 6. UTTERBACK GYM/{M A 7' TORNE'Y SOURCE United btatcs atent fifice 3,461,910 Patented Aug. 19, 1969 3,461,910 HYDROACOUSTIC AMPLIFIER Roger L. Sclsam and Max G.'Utterback, Monroe, N.Y.,

assignors to General Dynamics Corporation, a corporation of Delaware Filed June 2, 1966, Ser. No. 554,718 Int. Cl. E03b; 1503c; F17d 3/00 US. Cl. 137624.15 9 Claims ABSTRACT OF THE DISCLOSURE The hydroacoustic amplifier described herein includes a housing having a spool valve arranged in a stator port structure. The housing in which the valve is mounted defines four different cavities. Two of these cavities are at the opposite ends of the spool valve and are isolated from each other by the valve itself. The remaining two cavities are on opposite sides of a land which is located in the middle of the valve. Steady flow of pressurized fluid passes between the cavities on opposite sides of the land. An output cavity or line is connected between the cavities on opposite sides of the land. It is this cavity from which the acoustic power is derived and applied to a utilization device. Pressure is varied in one of the two end cavities by means of a stack of piezoelectric transducers which are driven by an electrical signal source. The spool valve is centered in the stator port region by means of lines which provide paths for steady flow from the steady fluid pressure source to the end cavities, while isolating the end cavities and the supply lines from each other with respect to varying or AC fluid pressure.

The present invention relates in general to a hydraulic system and more particularly to an improved hydroacoustic amplifier.

Although the present invention is suited for more general applications, such as in a hydraulic-mechanical motion amplifier, it is particularly adapted for use in a hydroacoustic amplifier, by which is meant a hydraulic system which controls fluid flow and/or pressure at a high power level at select frequencies in response to a low level input signal. Hydroacoustic amplifiers are particularly useful for underwater communications systems,

isince high levels of acoustic energy may be coupled to a power stage or to a load, such as surrounding water through a flexural disc or moving piston transducer. Some of the pressing problems of such systems are limited bandwidth, frequency range, harmonic distortion, and linearity, all of which are critical to fidelity of the signal reproduced, have limited the advancement and use of hydroacoustic amplifiers for underwater communication.

Accordingly, it is an object of the present invention to provide an improved hydroacoustic amplifier.

It is another object of the present invention to increase the frequency range of a hydroacoustic amplifier.

It is still another object of the present invention to provide an improved hydroacoustic amplifier with a greater bandwidth capability than previously obtained by prior art amplifiers.

It is yet another object of the present invention to provide improved linearity and the reduction of harmonic distortion in hydroacoustic amplifiers for improving the fidelity of signal reproduction.

It is a further object of the present invention to provide an improved hydroacoustic amplifier wherein a steady flow of fluid under pressure can be modulated inresponse to an input signal.

Briefly described, an improved hydroacoustic amplifier embodying the invention comprises a housing having first and second opposed cavities separated by a stator port structure and a pressure actuated valving member. The pressure actuated valving member is disposed in the stator port structure and responds to differences in press'ure in the first and second cavities by linear movement about a center position in the stator port structure. Also included is a means having an output chamber coupled to the stator port structure where acoustic energy is derived from the flow of fluid under pressure from inlet and outlet lines under the control of the valving member. Coupling means are connected to the output chamber for coupling the acoustic energy therein to the load. A first means is connected to the-inlet and outlet lines for establishing an average (DC) pressure in the first cavity. A second means is connected in the second cavity and communicates the pressure in the output chamber to the second cavity for establishing the same average (DC) pressure in the second cavity and restoring the valving member to the center position. Thus, the valving member is statically balanced between the first and second cavities by the same average pressure in the first and second cavities.

A signal means, such as a stack of piezoelectric elements is disposed in the first cavity for producing acoustic pressure variations with respect to the average pressure in response to an applied input signal to the elements. The stack of piezoelectric elements may have a larger diameter than the end of the valving member exposed to the first cavity, so that small linear displacements produced by the stack of piezoelectric elements results in a much greater displacement of the valving mcmber'in the stator port structure. The difference in diameter ratios results in a power transformation.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will become readily apparent from a reading of the following description in connection with the accompanying drawing which is a central, longitudinal, sectional view of a hydroacoustic amplifier in accordance with the invention.

A hydroacoustic amplifier is shown connected between a utilization device 3 and a pump 2 which supplies a fluid under pressure to the amplifier. The hydroacoustic amplifier produces acoustic energy from the steady flow of a fluid under pressure in an output chamber 4 in a manner to be described hereinafter. The pump 2 supplies the fluid under pressure to the amplifier through an inlet line 5 and the fluid is returned from the amplifier to the low pressure side of the pump 2 by way of an outlet line 6. The utilization device 3 may be any load, such as a power stage (not shown) in a two stage amplifier or other utilization devices, such as an underwater sound transducer having a piston or fiexural disc (not shown) which is vibrated in a longitudinal or flexural mode in response to fluid pressure variations in the chamber 4.

The hydroacoustic amplifier comprises a housing 10 having first and second cavities 11 and 12, respectively, separated by a stator port structure 13 and a valving member, such as a spool valve 14 slideably disposed in the stator port structure 13 and moveable about a center position. The spool valve 14 is shown in the drawing in the center position. The spool valve 14 has one end 15 slideably disposed in the first cavity 11 and the other end 16 slideably disposed in the second cavity 12. The valve 14 is movable about the center position in response to differences in pressure in the first and second cavities 11 and 12, respectively. In the operation of the hydroacoustic amplifier, the first and second cavities 11 and 12 are filled with a fluid under pressure. Assuming that the fluid pressure in the first cavity 11 is greater than the fluid pressure in the second cavity 12, the spool valve 14 is urged towards the second cavity 12, and conversely, if the pressure in the second cavity 12 is greater than the pressure in the first cavity 11, the spool valve 14 is urged or displaced towards the first cavity 11. The spool valve 14 is statically balanced when the pressure in the first and second cavities 11 and 12 are equal.

The spool valve 14 includes an annular land 17 disposed at a given point along its length. The stator port structure 13 includes an annular inlet chamber 25 and an annular outlet chamber 26 on opposite sides of the land 17. The land 17 and the ends 15 and 16 of the spool 14 are of equal cross section so that equal areas are exposed to the pressures in the chambers 25 and 26. The land .17 cooperates with the stator port structure 13 to form a variable annular inlet orifice 18 and a variable annular discharge orifice 19, both communicating with the output chamber 4. The annular inlct orifice 18 is formed by a lower edge 21 of the land 17 and a metering edge 22 of the stator port structure 13. The annular discharge orifice 19 is formed by an upper edge 23 of the land 17 and by another metering edge 24 of the stator port structure 13. The spool valve 14 is free to move axially within the stator port structure 13 in response to differences in pressure within the first and second cavities 11 and 12, to modulate the steady flow of fluid at an amplified power level from the inlet line 5 into the chamber 4 and discharge the fluid from the chamber 4 through the outlet line 6 to the low pressure side'of the pump 2.

The main hydraulic path of the fluid in the hydroacoustic amplifier may be traced by starting at the pump 2 which supplies the high pressure fluid, such as a low viscosity hydraulic oil or other suitable fluid medium. The fluid is pumped through the inlet line 5 to the annular inlet chamber 25 and through the annular variable orifice 18 into the chamber 4. The fluid is then returned from the chamber 4 to the low pressure side of the pump 2 by Way of the annular discharge chamber 26 and the outlet line 6.

The hydroacoustic amplifier includes a hydraulic centering means for the spool valve 14. The hydraulic centering means includes a secondary inlet line 51: connected between the inlet line 5 and the first cavity 11 and a secondary outlet line 6a connected between the first cavity 11 and the outlet line 6. The inlet line 511 and the outlet line 6a include flow restrictors 31 and 32, respectively, both of which have substantially the same resistance to fluid fiow or the same flow area for the passage of fluid from the inlet line 5 to the outlet line 6. The flow restrictors 31 and 32 are shown as being fixed area restrictors, however, it should be understood that adjustable restrictors may-be used to adjust the flow area to achieve the equal fiow areas or the resistance to flow between the restrictors 31 and 32. The combination of the restrictors 31 and 32 effectively acts as an hydraulic voltage divider wherein the pressure in the first cavity 11 is at an average or a half supply pressure (P /2) assuming the pressure in the outlet line 6 is at zero pressure. Assuming that the pressure supplied by the pump 2 is at' some pressure P and the pressure in the outlet line 6 is at some return pressure P the average (DC) pressure in the first cavity 11 may be expressed by the equation,

The centering means also includes a coupling line 33 having a restrictor 34 connected between the chamber 4 and the second cavity 12. The line 33 and the restrictor 34 communicate the fluid pressure in the chamber 4 to the second cavity 12. The edges 21 and 23 of the land 17 underlap the metering edges 22 and 24 respectively, of the stator port structure 13 so that the orifices 18 and 19 are partially opened and offer equal resistance to fluid flow into and out of thechamber 4, thus establishing the average pressure P in the chamber 4. The annular inlet and discharge orifices 18 and 19 respectively define another hydraulic voltage divider which establishes the same average pressure P or half supply pressure in the it I 3 second cavity 12. The fluid flow resistance of the restrictor 34 and the compliance of the cavity 12 are made relatively large so that AC pressure variations in the chamber 4 do not substantially affect the pressure in the second cavity 12. In efl'ect then, the combined resistance of the rcstrictor 34 and the compliance of the cavity 12 are likened to an RC circuit having a long time constant so that high modulation pressures or acoustic energy produced in the output chamber 4 do not substantially effect the average pressure previously established in the cavity 12.

The hydroacoustic amplifier further includes signal means such as a piezoelectric driver 40 for driving the spool valve 14 about the center position in response to an applied electrical input signal to terminals 41 and 42 from a signal source 39. The piezoelectric driver 40 includes a longitudinal stack of piezoelectric elements 43 electrically connected in parallel at electrodes 46 and 47, respectively, by leads 44 and 45. The leads 44 and 45 are insulated from the housing 10 at 54 and 55. The leads 44 and 45 are connccted to the input terminals 41 and 42, respectively. The stack of piezoelectric elements 43 vibrate mainly in a thickness mode in response to an electrical input signal ap plied to terminals 41 and 42. The stack of piezoelectric elements 43 may be polarized so that they may contract and expand about a reference thickness. The piezoelectric driver'40 also includes a piston 48 coupled to the stack of piezoelectric elements 43 by an elastic or resilient rod 49 connected to the housing 10. The piston 48 is disposed in the first cavity 11 and may induce positive and ncga-.

tive pressure variations Within the first cavity 1.1 whenever the stack of piezoelectric elements 43 is excited by an electric input signal. The piston 48 has a larger diameter or area than the diameter or area of the one end 15 of the spool valve 14. In accordance with the invention, hydraulic transformation is achieved by this difference in area between the one end 15 of the spool valve 14 and the piston 48. Relatively small displacement of the piston 48 in the cavity 11 results in a much larger displacement of the spool valve 14. In some cases, the piston 48 may be eliminated and the piezoelectric elements 43 may act directly on the fluid in the first chamber 11. A fluid seal, such as an O-ring 51, is provided between the piston 48 and the cavity 11.

In the quiescent operation of the hydroacoustic amplifier 1, the pump 2 supplies a steady flow of fluid under pressure to the amplifier through the inlet line 5. The fluid is returned to the pump 2 from the amplifier by way of the outlet line 6. In the absence of a signal at input terminals 41 and 42, the spool valve 13 is automatically statically balanced within the stator port structure 13 at a center position. This center position of the spool valve 14 is shown in the drawing and is achieved by deriving the same average pressure (P in the first and second cavities 11 and 12. The average pressure P is achieved in the first cavity 11 by the equal flow areas or fluid flow resistance of the restrictors 31 and 32 in lines 5a and 6a respectively, as previously described.

The average pressure P in the second cavity 12 i achieved by the bypassing of fluid under pressure through the variable annular inlet orifice 18 and the variable an nular discharge orifice 19 into and out of the output chamber 4.

The pressure in the output chamber 4 is directly related to the opening or flow areas of the inlet and discharge orifices 18 and 19 respectively. Assuming that the spool valve 14 is displaced towards the second cavity 12 and the inlet orifice 18 is opened while the discharge orifice v 19 is closed, the pressure in the chamber 4 will approach the supply pressure P of the pump 2. The pressure which exists in the output chamber 4 is communicated to the second cavity 12 by way of the line 33 through the high resistance-to-flow restrictor 34. Since the supply pressure I is greater than the average pressure P the spool valve 14 is urged towards the first cavity 11 by the difference in pressure which exists between the first and second cavities 11 and 12. As the spool valve 14. moves towards the first cavity 11, the flow area of the inlet orifice is reduced and consequently, the pressure in the output chamber 4 and the second cavity 12 is also reduced. The reduction of pressure in the output chamber 4 and in the second cavity 12 continues until the How area of the inlet orifice 18 equals the flow area of the discharge orifice 19 whereby the pressure in the output chamber 4 and the second cavity 12 reduce to the average pressure P At this point, the spool valve 14 is statically balanced and centered in the stator port structure 13. A steady or DC flow of fluid under pressure continuously flows through the output chamber 4 by way of the inlet and discharge orifices 18 and 19 respectively, to maintain the average pressure P in the output chamber 4. In accordance with the invention, the average pressure P is communicated from the chamber 4 to the second cavity 12 during operation of the amplifier. As previously mentioned, the restrictor 34 has a high resistance R to fluid flow and the second cavity 12 has a high compliance C which together with the restrictor 34 define the hydraulic circuit which has a high time constant. This is likened to an electrical RC circuit. The significance of the high time constant RC circuit is that the pressure transients or variations in the output chamber 4 substantially expire during the time of the time constant. Thus, the average pressure P, in the second cavity 12 remains relatively unellected during the quiescent or active operation of the amplifier.

In the active operation of the amplifier, electrical signals are applied to the input terminals 41 and 42 from the signal source 39. The electrical input signals excite the piezoelectric elements 43 into vibration principally in a thickness mode at the frequency and amplitude corresponding to the input signal. When the stack of piezoelectric elements 43 are excited in a thickness mode, the piston 48 in the firstcavity 11 varies the fluid pressure therein by an amount proportional to its displacement. The spool valve 14 in response to the induced pressure variations, in the first cavity 11, is displaced towards or away from the second cavity 12 depending upon whether the induced pressure variations in the first cavity 11 are above or below the average pressure P Assume by way of example, that a sine wave input signal is applied to the driver 40. It should be understood, however, that other input signals of various frequencies and amplitude may be applied to the input terminals 41 and 42 for transduction into corresponding pressure variations or acoustic energy in the output chamber 4 for use in the utilization device 3. The pressure in the first cavity 11 may be, for example, increasing while the signal is positive-going and decreasing when the signal is negative-going. Considering a positive-going signal, the piezoelectric elements 43 expand and push the piston .48 into the first cavity 11, increasing the pressure therein above the average pressure P In response to the increased pressure in the first cavity 11, the spool 14 is displaced towards the second cavity 11, opening the inlet orifice 18 and closing the discharge orifice 19 in an amount directly proportional to the increased pressure. When the inlet orifice 18 is opened further, the

m pressure in the chamber 4 increases by a corresponding amount. The opening of the inlet orifice 18 continues to the peak voltage of the input signal.

When the input signal starts to go negative, the pressure in the first cavity decreases and the pressure in the second cavity 12 urges the spool valve 14 to move in a direction towards the first cavity 11. When the spool valve 14 is urged towards the first cavity 11, the flow area of the inlet orifice 18 is decreased, while the flow area of the discharge orifice 19 is increased. Thus, the spool is acted upon by a positive difference in pressure on the one end 16 and the other end of the spool valve 14. The opening of the discharge orifice 19 causes the pressure in the output chamber 4 and the second cavity 12 to decrease until the average pressure is restored in the output chamber 4 and the second cavity 12. In this case, the spool valve 14 has been returned to the center position and may now be urged towards the first cavity 11 if the pressure in the first cavity 11 drops below the average pressure. The spool valve 14 thus follows the negativegoing signal and may continue to do so until the negative peak voltage of the signal is reached. When the inlet orifice 18 is completely closed, the pressure in the chamber 4 and the second cavity 12 drops towards the return pressure P,.

If the above described motions of the spool valve 15 and resulting pressure variations in the chamber 4 occur in a short time compared to the RC time constant previously described as being defined by the fiuid restrictor 34 and the fluid filled second cavity 12, these pressure motions do not significantly affect the average pressure in the second cavity 12, and the centering means continues to operate to maintain the valve 14 positioned in the center position and the average pressure P in the chamber 4 as previously described. Thus it may be seen that the spool valve 14 follows the input signal applied to the piezoelectric elements 43. The spool valve 14 is continuously urged, however, towards the center position in the stator port structure 13 by the centering means of the amplifier.

While a preferred embodiment of the invention has been described, it should be understood that variations and modifications thereof within the spirit of the invention will undoubtedly suggest themselves to those skilled in the art. For example, the piston 48 may be driven by a magnetostrictive driver instead of a piezoelectric driver 40. Accordingly, the description should be taken merely as illustrative and not in any limiting sense.

What is claimed is: I

1. A hydroacoustie amplifier comprising (a) a housing having first and second cavities separated by a stator port structure,

(b) inlet and outlet lines for the passage of fluid under pressure into and out of said housing through said stator port structure, I

(c) a pressure actuated valving member disposed in said stator port structure and isolating said first and second cavities from each other and responsive to differences in pressure in said first and second cavities for linear movement about a position in said stator port structure,

(d) means isolated from said first and second cavities by said valving member including a chamber coupled to said stator port structure for deriving acoustic energy therein from the How of the fiuid through said inlet and outlet lines under the control of said valving member,

(e) first means connected to said inlet and outlet lines for establishing an average DC pressure in said first cavity,

(f) second means connected to said second cavity and.

responsive to the pressure in said said chamber for establishing said (DC) average pressure in said second cavity while blocking varying flow of fluid at acoustic frequency to said second cavity, and

(g) signal means in said first cavity coupled to said valving member solely via said fluid in said first cavity for producing acoustic frequency pressure variations about said (DC) average pressure in said first cavity in response to a varying input signal applied thereto whereby said valving member responds only to said acoustic frequency pressure variations in said first cavity.

2. The invention defined in claim 1 wherein said first means includes first and second lines each having substantially equal area restrictors connected between said first cavity and said inlet and outlet lines respectively.

3. The invention defined in claim 1 wherein said second means includes a coupling line having a fiuid fiow structure therein for restricting the flow of fiuid between said chamber and said second cavity having a high compliance whereby said restrictor in said coupling line and said second cavity define an RC hydraulic circuit having a high time constant.

4. The invention defined in claim 1 wherein said signal means includes at least one piezoelectric element in said first cavity for producing said pressure variations in response to said input signal.

5. The invention defined in claim 1 wherein said signal means includes a plurality of piezoelectric elements connected in cooperative relationship with each other for varying said fluid pressure in said first cavity in response to said input signal.

6. The invention defined in claim 1 wherein said sig nal means includes a piston disposed in said first cavity and defining a portion of a wall thereof and a plurality of piezoelectric elements connected in cooperative relationship with said piston for reciprocating said piston and varying said fluid pressure in said first cavity in response to said input signal.

7. The invention as set forth in claim 1 wherein said signal means includes a plurality of piezoelectric elements defining a piston of a given cross-sectional area in said first cavity and the end of said valving member in said first cavity having a cross-sectional area smaller than said given cross-sectional area of said piston whereby small displacement of said piston results in a larger displacement of said valving member than the displacement of said piston.

8. The invention defined in claim 1 wherein said signal means includes an electrically responsive element in said one cavityjor producing said pressure variations in response to said input signal.

9. The invention as set forth in claim 6 wherein said piezoelectric elements are arranged in a stack terminated at one end by said piston to acoustically vary the pressure in said first and second cavities upon reciprocation of said stack.

References Cited UNITED STATES PATENTS 2,824,292 2/1958 Christoph 13782 X 2,895,061 7/1959 Probus 18l.5 X 3,054,592 9/1962 Christoph 181-.5 X 3,055,383 9/1962 Paine 13785 3,063,422 11/1962 Gregowski 137-82 X 3,286,719 11/1966 Myers 137-83 3,286,734 11/1966 Hartshorne 137-62564 ALAN COHAN, Primary Examiner US. Cl. X.R. 137-625.64, 625.66 

